Extensive spin-orbit multi-reference computations on the excited states of the phosphorus monochloride molecule

- The PECs of the 34 Λ-S states of the PCl molecule have been calculated.
- The couplings between the states have been studied with SO matrix elements.
- This is the first time that the SOC effect of PCl has been studied.
- The PECs of the 74 Ω states arising from the 34 Λ-S states have been calculated.
- The E1, M1, and E2 transition probabilities has been calculated.

Total 34 Λ-S states of the PCl molecule have been studied by using the multi-reference configuration interaction plus the Davidson correction (MRCI+Q) method with the correlation consistent quadruple-zeta quality basis set. These states are correlated to three dissociation limits P(4Su)+Cl(2Pu), P(2Du)+Cl(2Pu), and P(2Pu)+Cl(2Pu), respectively. The potential energy curves (PECs) of the Λ-S states have been calculated, from which the spectroscopic constants of the bound states are determined. The calculated spectroscopic results well reproduce the available measurements. The spin-orbit matrix elements between the Λ-S states have been calculated, which indicate that the perturbations exist in the interacting system 11Π−23Π and 11Π−23Σ−. And the excited a1Δ, b1Σ+, 21Σ+ states could be predissociated induced by the spin-orbit coupling (SOC) effect. The SOC calculation on the PCl molecule has been performed with the state interaction method. This is the first time that the SOC effect of the PCl has been studied theoretically. The SOC effect leads to the 34 Λ-S states split into the 74 Ω states. The ground state X3Σ− splits into the X3Σ0−+(X10+) and X3Σ1−(X21) states. For the zero-field splitting of the X3Σ− state, the spin-orbit contribution of 6 cm−1 is much larger than spin-spin contribution of 0.32 cm−1. Under the influence of the SOC effect, the spectroscopic results of the a1Δ and b1Σ+ states have very small changes, but the dissociation energies strongly decrease. The transition properties of PCl are also predicted, including the E1, M1, and E2 transition moments, the Franck-Condon factors, the transition probabilities, and the radiative lifetimes. For the transitions from a1Δ-X3Σ− and b1Σ+−X3Σ−, the transition probabilities are in order of AE1 > AM1 ≫ AE2. The lifetimes for the b1Σ+(v׳=0) state are 4.87ms (E1) and 4.57 ms (E1+M1), in good agreement with the available experimental result of 4.9±0.8 ms.

The enlarged view of the E1TMs of the selected transitions around the avoided crossing points.185